Epoxy question

[JohnD]

I am in the process of building a new icebox for my Triton. I have all the insulation in as well as some 1/4" plywood over it for some support. Once done with the epoxy work I will be laying down some fiberglass on top of this and then painting it. Yesterday I coated the wood with some epoxy, but looking at it today I seem to have missed a couple of spots, and not done nearly as well as I hoped for rounding out the edges.

My question is, do I need to sand down this coat before adding another layer, or can I just put down another coat in a day or two?

As you can probably tell, this is my first time working with epoxy. I feel a little silly asking something that is more than likely very obvious to you guys. Complete newbie to the boat thing here so please bear with me.

[Rachel]

Hi John,

Much better to ask than to forge ahead and possibly have a failure that is a pain to deal with! I use epoxy reasonably often, but it's still infrequently enough that I find my self referring back to written literature, or searching here to review a step or two.

Basically, you have a window in which you can make a chemical (primary) bond, and as long as you are in that window you can just put more on top of what you have. This is also called the "green stage." Once that window has closed, you have to let it fully cure, remove any amine blush, sand for tooth, clean/de-dust, and then you can put more on (this time it is a mechanical, or secondary bond).

The end of the green stage is a bit of a grey area in my mind. I know that as long as you can still dent it with a thumbnail you are still good to overcoat, but I have never been completely sure if there is still any window after that (so I just make sure to either work within that time frame or let it cure and use plan B). I am pretty sure 2-3 days would be too long (of course this is somewhat temperature dependent, as a really cold shop would prolong it), but I'll be interested to hear what the people who use epoxy more have to say about how long they extend that "green" window.

For general info, here are a couple of free publications that I find helpful:

1) WEST System's epoxy manual
You can pick this up as a free booklet oftentimes at places that sell WEST, but at this link each illustration leads to one "chapter" of the manual. This information is not really WEST specific (except for mixing ratios and certain specific products).

http://www.westsystem.com/ss/use-guides/

2) System Three's "The Epoxy Book," available here in .pdf to download, also free:

http://www.systemthree.com/reslibrary/l ... y_Book.pdf

Rachel

PS: I came back to add (since you said this is your first time working with epoxy) that it's important to work "clean" with epoxy. You may already be doing this, I realize. The thing is, even though epoxy doesn't smell really strong, like polyester or etc. it can still sensitize your skin (after which you have to be *really* careful, so best not to go there), and the dust is not good to breathe.

So, just take care to always wear gloves and (especially when sanding) a respirator, plus other appropriate safety gear. I like to don three disposable nitrile gloves on each hand, and then I can just peel them off as they get gunky and, voila!, there is a clean one. I found that I was often doing just great until it came time to change gloves, and then I would get a dollop of epoxy on my skin, so that's when I went to the three glove method.

[Duncan]

John, the curing depends on temperature as well as which epoxy and hardener, but it sounds like you should treat it as a secondary bond at this point. It sounds like you are doing a careful job, so better to not take any chances.

...I like to don three disposable nitrile gloves on each hand, and then I can just peel them off as they get gunky and, voila!, there is a clean one. I found that I was often doing just great until it came time to change gloves, and then I would get a dollop of epoxy on my skin, so that's when I went to the three glove method.

That's simple and brilliant, thanks, Rachel. "Good Tip of the Week" award goes to you.

[JohnD]

Thank you for your replies. After reading your recomendations and the fact that I just got off a 24 hour shift I will be doing the secondary bonding. I'm hoping that after my nap when I head out there it will be cured enough to do some sanding.

Love the glove trick. So much easier than pealing off a messy pair and trying to put a clean one on.

[JohnD]

Again, thank you guys for your advice. I have the inside all sealed up and the second coat sanded smooth and ready to continue. Now I have another question in regard to the icebox.

Why do we lay cloth on top of this, for extra support? It seems pretty solid now and I kind of like the way it looked showing the wood through the epoxy. Is there any reason not to just add another coat and leave it llike that?

[Quetzalsailor]

Now I tell you...you coulda' laid the cloth into your first coat on the wood. Then subsequent coats are applied to fill the weave as necessary. You would add a cloth layer for the same reason that the stripper canoe builders do. The cloth ensures that the covering is less damaged when dinged and ensures greater film thickness. The stripper canoe also gets its transverse fiber out of the cloth. If you use light cloth, you'll hardly see it; barely a ghost of the fibers.

[Rachel]

"Cloth" will add strength and is what really makes it "fiberglass." Resin alone has some uses, but it is just resin. It's a coating that can be used for certain purposes, but does not - alone - impart strength. A thin coating of resin is fairly flexible; a thicker layer of resin alone is rather brittle.

So, say you are coating the end grain of a piece of plywood and will later paint over it. Then resin is okay. If you are going to be dumping blocks of ice, onto the face of that same piece of plywood, I would want to reinforce it with cloth.

Another example is if you have fir plywood on the exterior of something (which... I would choose something else, but as an example). If you coat it with resin, it will later check. If you coat it with resin and a layer of (even relatively thin) 4 oz. cloth... no checking.

Back to your icebox: I'm just curious -- and we don't know all the details of your construction of course -- but if you only have plywood and resin, how are you sealing the joints (say, where the bottom joins the sides)? I would most likely coat the wood with resin, then lay in thickened epoxy fillets on all of those seams and corners, then tab them/lay fiberglass cloth over all, and then fair. And later paint or gelcoat.

Rachel

[JohnD]

"Back to your icebox: I'm just curious -- and we don't know all the details of your construction of course -- but if you only have plywood and resin, how are you sealing the joints (say, where the bottom joins the sides)? I would most likely coat the wood with resin, then lay in thickened epoxy fillets on all of those seams and corners, then tab them/lay fiberglass cloth over all, and then fair. And later paint or gelcoat.
Rachel

That is exactly what I am doing. I already have the fillets done and am to the point where I need to go buy some cloth. Thanks for the answers and suggestions. Not sure how well the pictures will show here, but i think you can see in the second photo how it is progressing. The first one just shows the drain position. I just like the look of the wood and was wondering if it was possible to keep it that way. I guess not, but I'm glad I asked.

[Rachel]

Okay, I see - thanks for the photos. It does look nice like that :)

But... yes, I would go on and tab/cloth/fair and then paint or gelcoat. I wouldn't want to have to "baby" an icebox and even if there was not an obvious failure at some point in time, I would be worried about some unseen split or separation causing a leak that would only be detected after you smelled moldy insulation or something... Ugh.

What is that in the lower left corner of the first photo? It looks like maybe a drain but then - at least to me in the photo - it looks like it sticks up, so I'm just curious about what I'm seeing there.

Rachel

[Duncan]

... I just like the look of the wood and was wondering if it was possible to keep it that way. I guess not, but I'm glad I asked

If you don't paint it, I imagine the wood would show through a thin layer of fiberglass quite nicely.
Epoxy resin is food-safe, so isn't it just as good as paint?

[JohnD]

Rachel, it is a drain. It just happens to be sticking up a bit because it is just sitting in place in that picture. It will be flush with the bottom when it is finished.

Duncan, thanks for the tip. No paint it is!